FORT EDWARD, NY.- A mistake made along the Hudson River is offering archaeologists a rare glimpse into how colonial military engineers built wooden forts, including the key stronghold constructed here by the British during the French and Indian War.

A formal excavation of the original Fort Edward was called after crews dredging PCB-contaminated sediment from the Hudson River last month accidentally ripped out wooden beams thought to have been part of the original fort, which was built in the 1750s. Redcoats, rangers, American Indians and settlers mingled at the site as England and France fought for control of North America.

Archaeologists, after spending two weeks scraping away layers of soil from the river's steep east bank, have uncovered more evidence of the foundation of what was once Britain's largest fortification on this continent.

"There's absolutely no doubt that this is part of Fort Edward and these timbers are specifically from the water bastion," said nautical archaeologist Adam Kane, referring to the southwest section of the fort that jutted into the river.

Although just a dot on 18th-century maps of the northern New York wilderness, Fort Edward was known to common soldiers and kings during the French and Indian War (1754-63), when it blocked French movement south toward Albany. Newspapers and magazines in the American colonies and England published dispatches from the fort, manned by thousands of British regulars and colonial militia and a base of operations for the famed Rogers' Rangers.

The French never launched a direct attack but soldiers and officers posted here often wrote home about the grisly aftermath of frequent Indian ambushes sprung outside the walls.

"A lot of the action that people read about took place between here and Lake George," said Charles Vandrei, historic preservation officer for the state Department of Environmental Conservation.

The DEC and the U.S. Environmental Protection Agency are overseeing the archaeological work that began earlier this month, three weeks after the mistake by a dredging crew contracted by General Electric as part of the company's $750 million project to remove PCBs, or polychlorinated biphenyls, from the river. PCBs, used as coolants and lubricants for years, were dumped into the Hudson by a GE factory in Fort Edward and another nearby. The chemical, banned in 1977, is a suspected carcinogen.

Dredging was temporarily suspended in August after potentially dangerous levels of PCBs kicked up by the activity drifted downstream. Only days after the dredging resumed, the wooden beams were ripped from the riverbank.

Locals insisted the removed beams were from the original fort, while some experts thought the timbers could have been part of a later structure. Examination of the beams has pegged them to the fort's construction period of 1755-58, said Kane, a nautical archaeologist with the Lake Champlain Maritime Museum in Vergennes, Vt.

The beams pulled from the fort site will be analyzed for PCB contamination to determine whether they can be publicly displayed, said John Vetter, the EPA archaeologist at the site.

Meanwhile, the excavation is revealing how military engineers built large fortifications in a wilderness where resources were few and soldiers were the only source of labor.

The biggest surprise so far is the discovery of "sleeper" timbers, 3-foot-long, hand-hewn crossbeams placed on the river bottom. Kane said sleeper timbers served as a base similar to railroad ties, with longer beams placed perpendicular on top to form the water bastion's outer walls.

The museum's marine archaeologists found the sleeper timbers submerged in shallow water, under a longer beam protruding from the bank into the river. Archaeologists say the wet, muddy conditions have helped preserve the wood, which still bears the ax marks made by the colonial troops who built the fort.

The underwater work has given way to a land-based excavation being conducted by archaeology consultants from San Francisco-based URS Corp., hired by GE to handle excavations along this history-rich stretch of river.

Other than the beams that were removed from the site and the timbers that remain there, no other artifacts dating back to the fort's early years have been recovered. Dan Cassedy, who's leading the dig for URS, expects that to change as the dig progresses deeper into the river bank.

Property owner Neal Orsini was incensed at first to learn that the beams had been ripped out of his river bank, since he had previously alerted GE's dredging managers to their location. But like others involved in the dig, he now sees this as an opportunity to learn more about the old fort while drawing attention to the community's colorful history.

"Both personally and community-wise, we're trying to make the best of a difficult situation," said Orsini, a town board member and restaurant owner. "As long as they make my river bank pretty again, I'll be happy with that."

"We think it's wonderful," said neighbor JoAnne Fuller, a French and Indian War buff who lives in a house built on the site of the old fort. Her home is filled with maps, books, journals, muster rolls and artwork pertaining to the war, and her husband Richard has built detailed scale models of the fortification, right down to the bunk beds in the fort's smallpox hospital.

"We're obsessed," Richard Fuller said. "Sitting on history has given us the impetus to do a lot of this stuff."

The fort fell into disrepair after the war ended in 1763 with France handing over Canada to the British, and the village of Fort Edward grew up on the site. Previous archaeological digs uncovered buried remnants of the fort, while excavations on neighboring Rogers Island found evidence of barracks and other structures.

The island is named for Maj. Robert Rogers of New Hampshire, leader of Rogers' Rangers, the British army's main scouting unit. It was there, in the fall of 1757, that Rogers wrote a list of rules for wilderness fighting. His "Rules for Rangering" would find their way into Army Ranger training manuals two centuries later, and they're still used by today's U.S. Special Forces.